For many years glass used in buildings and automobiles has been coated to reduce transmission of heat. From the inception of coating such glass, the coating has functioned to exclude infrared energy from the sun. This is extremely effective in reducing the thermal input to buildings and automobiles with large areas of glass exposed to sunlight. Such coatings are most effective in the summer months and definitely reduce heat loads for air conditioning systems. The coatings used have been varied and examples are gold, titanium nitride, indium oxide and indium tin oxide. Such coatings usually are applied to the outer surface of the glass or the inside of the outermost layer of the glass. Because of this location of the coating, it is not particularly effective in reflecting heat back into the building or into the automobile during winter months. An additional undesirable effect of the use of such coatings is that during winter months, infrared energy from the sun continues to be reflected when it could well be used to provide heat for the occupants of the building or automobile equipped with such coated glass during hours of strong sunlight.
Present coatings for architectural glass are only about 75 percent as effective as they could be in concept and realistically are slightly less than 27 percent effective when considered over a full annual period in the middle United States region. The effectiveness of these coatings decreases the further north they are used and increases the further south they are used. While such coatings are effective in reflecting infrared energy, they also significantly reduce the transmission of solar energy in the visible spectrum. This can be an objectionable consideration for many uses.